The present invention relates to a method of making an aggregate using a multi-stage process. In particular, the process relates to a method of making an aggregate comprising at least a carbon phase and a silicon-containing species phase using a multi-stage reactor. The present invention also relates to a method of making an aggregate comprising a carbon phase and a metal-containing species phase. The present invention in addition relates to the use of one or more of these aggregates in compositions such as elastomeric compositions and further relates to methods to improve rolling resistance and wet traction for tire compounds and relates to elastomeric compositions having these properties.
Carbon blacks are widely used as pigments, fillers, and reinforcing agents in the compounding and preparation of rubber and other elastomeric compounds. Carbon blacks are particularly useful as reinforcing agents in the preparation of elastomeric compounds used in the manufacture of tires.
Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black. Carbon black exists in the form of aggregates. The aggregates, in turn are formed of carbon black particles. However, carbon black particles do not generally exist independently of the carbon black aggregate. Carbon blacks are generally characterized on the basis of analytical properties, including, but not limited to, particle size and specific surface area; aggregate size, shape, and distribution; and chemical and physical properties of the surface. The properties of carbon blacks are analytically determined by tests known to the art. For example, nitrogen adsorption surface area (measured by ASTM test procedure D3037-Method A or D4820-Method B) and cetyl-trimethyl ammonium bromide adsorption value (CTAB) (measured by ASTM test procedure D3765 [09.01]), are measures of specific surface area. Dibutylphthalate absorption of the crushed (CDBP) (measured by ASTM test procedure D3493-86) and uncrushed (DBP) carbon black (measured by ASTM test procedure D2414-93), relates to the aggregate structure. The bound rubber value relates to the surface activity of the carbon black. The properties of a given carbon black depend upon the conditions of manufacture and may be modified, e.g., by altering temperature, pressure, feedstock, residence time, quench temperature, throughput, and other parameters.
It is generally desirable in the production of tires to employ carbon black-containing compounds when constructing the tread and other portions of the tire. For example, a suitable tread compound will employ an elastomer compounded to provide high abrasion resistance and good hysteresis balance at different temperatures. A tire having high abrasion resistance is desirable because abrasion resistance is proportional to tire life. The physical properties of the carbon black directly influence the abrasion resistance and hysteresis of the tread compound. Generally, a carbon black with a high surface area and small particle size will impart a high abrasion resistance and high hysteresis to the tread compound. Carbon black loading also affects the abrasion resistance of the elastomeric compounds. Abrasion resistance increases with increased loading, at least to an optimum point, beyond which abrasion resistance actually decreases.
The hysteresis of an elastomeric compound relates to the energy dissipated under cyclic deformation. In other words, the hysteresis of an elastomeric composition relates to the difference between the energy applied to deform the elastomeric composition and the energy released as the elastomeric composition recovers to its initial underformed state. Hysteresis is characterized by a loss tangent, tan xcex4, which is a ratio of the loss modulus to the storage modulus (that is, viscous modulus to elastic modulus). Tires made with a tire tread compound having a lower hysteresis measured at higher temperatures, such as 40xc2x0 C. or higher, will have reduced rolling resistance, which in turn, results in reduced fuel consumption by the vehicle using the tire. At the same time, a tire tread with a higher friction coefficient on a wet surface will result in a tire with high wet traction and wet skid resistance which will increase driving safety. Thus, a tire tread compound demonstrating low hysteresis at high temperatures and high hysteresis at low temperatures can be said to have a good hysteresis balance.
There are many other applications where it is useful to provide an elastomer exhibiting a good hysteresis balance but where the abrasion resistance is not an important factor. Such applications include but are not limited to tire components such as undertread, wedge compounds, sidewall, carcass, apex, bead filler and wire skim; engine mounts; and base compounds used in industrial drive and automotive belts.
Silica is also used as a reinforcing agent (or filler) for elastomers. However, using silica alone as a reinforcing agent for elastomer leads to poor performance compared to the results obtained with carbon black alone as the reinforcing agent. It is theorized that strong filler-filler interaction and poor filler-elastomer interaction accounts for the poor performance of silica. The silica-elastomer interaction can be improved by chemically bonding the two with a chemical coupling agent, such as bis(3-triethoxysilylpropyl)tetra-sulfane, commercially available as Si-69 from Degussa AG, Germany. Coupling agents such as Si-69 create a chemical linkage between the elastomer and the silica, thereby coupling the silica to the elastomer.
When the silica is chemically coupled to the elastomer, certain performance characteristics of the resulting elastomeric composition are enhanced. When incorporated into vehicle tires, such elastomeric compounds provide improved hysteresis balance. However, elastomer compounds containing silica as the primary reinforcing agent exhibit low thermal conductivity, high electrical resistivity, high density, and poor processability.
When carbon black alone is used as a reinforcing agent in elastomeric compositions, it does not chemically couple to the elastomer but the carbon black surface provides many sites for interacting with the elastomer. While the use of a coupling agent with carbon black might provide some improvement in performance to an elastomeric composition, the improvement is not comparable to that obtained when using a coupling agent with silica.
The present invention relates to a method of making an aggregate comprising at least a carbon phase and a silicon-containing species phase. In the method, for a two stage feedstock injection system, a first feedstock is introduced into a first stage of a multi-stage reactor. The first feedstock comprises a carbon black-yielding feedstock, a silicon-containing compound or a mixture thereof. The method further includes the step of introducing a second feedstock into the reactor at a location downstream of the first stage. The second feedstock comprises a carbon black-yielding feedstock, a silicon-containing compound, or a mixture thereof, with the understanding that if the first feedstock comprises only a carbon black-yielding feedstock (without a silicon-containing compound), then the second feedstock comprises either a mixture of a carbon black-yielding feedstock and a silicon-containing compound or silicon-containing compound alone. At least one feedstock, either the first feedstock or the second feedstock, comprises at least a carbon black-yielding feedstock and at least one of the feedstocks, the first or the second feedstock, comprises a silicon-containing compound. However, the number of stages can be any number but must be at least two. The multi-stage reactor is maintained at a sufficient temperature to decompose the silicon-containing compound and to pyrolize the carbon black-yielding feedstock.
The present invention further relates to a method of making an aggregate comprising a carbon phase and a silicon-containing species phase, wherein a multi-stage reactor is used having at least three stages for introducing feedstocks into the reactor. The second and third stages as well as any additional stages are located downstream of the first stage. Each of the feedstocks introduced into the stages comprises a carbon black-yielding feedstock, a silicon-containing compound, or a mixture thereof. At least one of the stages comprises a carbon black-yielding feedstock and at least one of the stages comprises a silicon-containing compound. The reactor is maintained at a sufficient temperature to decompose the silicon-containing compound and to pyrolize the carbon black-yielding feedstock.
The aggregates of the present invention preferably have a rough surface measured by the difference between BET (N2) surface area and t-area of the aggregate. Upon HF (hydrofluoric acid) treatment, BET area and t-area of this aggregate preferably increases. The aggregate size after HF treatment measured by DCP (Disc centrifuge photosedimentameter) may be generally reduced, and a certain amount of silica remains in the aggregate. The silica remaining after thermal treatment of the carbon phase at 500xc2x0 C. in air preferably has a high surface area.
In addition, the present invention relates to a method of making an aggregate comprising a carbon phase and a metal-containing species phase wherein a multi-stage reactor is used having at least two stages for introducing feedstocks into the reactor. The second stage as well as any additional stages are located downstream of the first stage. Each of the feedstocks introduced into the stages comprises a carbon black-yielding feedstock, a metal-containing compound, or a mixture thereof. One or more of the feedstocks further optionally comprises a silicon-containing compound. At least one of the stages comprises a carbon black-yielding feedstock and at least one of the stages comprises a metal-containing compound. The reactor is maintained at a sufficient temperature to decompose the metal-containing compound and to pyrolize the carbon black-yielding feedstock.
The aggregates made from the above-described methods can be incorporated into elastomeric compositions. These elastomeric compositions can provide improved wet skid resistance and rolling resistance compared to elastomeric compositions not having any aggregates comprising a carbon phase and a silicon-containing species phase present.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed. Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the written description and appended claims.
The accompanying drawing, which is incorporated in and constitutes a part of this specification, illustrates an embodiment of the present invention and together with the description, serves to explain the principles of the present invention.